Re: How you send a receipt to your client?
Congrats on the new client!!
Receipts are something you wouldn't send out very often - unless the client specifically requests one. Generally the tax invoice becomes receipt once payment has been made.
I do my receipts in Word. They have their own numbering system, the space where you put all the details etc, and I also put the method of payment (cheque, bank transfer, paypal etc). At the bottom I also have 'Thank you for your business'.